1. Field of the Invention
This invention relates to processing of call related operations at base stations of a cellular wireless communication system, and particularly to a processing management scheme that insures a base station will maintain its ability to process user call activities while handling an increasing number of active calls.
2. Discussion of the Known Art
A typical base station of a cellular wireless communication system has processing equipment that controls call-related activities such as, for example, call originations, call terminations, handoffs of active calls to or from the base station, and user registrations and paging. These activities all use or occupy processing time at the base station. For example, at base stations of code division multiple access (CDMA) systems, processing equipment known as a radio control complex (RCC) includes a number of associated hardware units that interface with a system bus with which a core processor unit (CPU) is connected. As user activity in a base station's area of coverage or "cell" increases, the RCC approaches a limit of its maximum capacity to handle both new and ongoing traffic functions. Co-pending U.S. patent application Ser. No. 09/131,390 filed Aug. 7, 1998, entitled "CDMA Base Station Assisted Soft Handoff" and assigned to the assignee of the present invention and application, discloses a scheme for conserving base station processing resources and available forward link power. All relevant portions of the mentioned patent application are incorporated by reference. Specifically, the scheme proposes a reduction of call handoff activity at a CDMA base station. That is, a user who might add a new base station to a list of potential base stations to which the user may be handed off, is maintained by only currently serving CDMA base stations as long as a minimum quality of call service is being provided.
Although a CDMA base station preferably should support multiple carriers at its site to allow for potential subscriber growth, current limitations of base station processors including the mentioned RCC, make it difficult at present to support more than three carriers in a CDMA system. User-related control functions that contribute significantly toward RCC processing time at a CDMA base station include, for example, handoffs of calls to or from the base station, or between sectors of the same base station; subscriber call originations (i.e., attempts by a user to initiate a call via the base station); and user call termination (i.e., connection of a call originating from a wired (telephone) network with which a base station is linked, to a user in the base station's cell). Each handoff typically occupies about 100 milliseconds of processing time at the base station. Each call origination and termination occupies about 75 milliseconds. User registration (i.e., system recognition of a user prior to placing or receiving a call), and paging of a user with operating data from the base station, each occupy about five milliseconds of the base station's processing time. Processing times may vary depending on the CPU used at the base station.